Hi Vance,
Thanks for the response. I appreciate it.
My real concern is cost and value.
This is a street engine -- about 3000 miles per year. I don't want to be
at the hairy edge and be rebuilding every 6000 miles.
I have been told to keep the valve lift not much over .425, and keep the
RPM under 6000. I believe I can use the later stock TR6 dual springs at
.425 valve lift (0 lash -- not net).
I can get the .425 with a cam with small bumps and 1.65:1 roller rockers
or I can get a cam with big bumps designed for standard 1.45:1 rockers.
I believe staying under 6000 rpm will help with the 1.45:1 cam's big
bumps. The head will 9.5 to 9.8 somewhere in there -- not over 10.0.
Good for 93 octane so I am told.
It's $500 for the 1.45:1 cam and a new set of standard rockers vs $800+
for the cam and 1.65:1 roller rockers. Both cams will be from chilled
cast iron billets -- not regrinds.
Also, is it wise to use my old rockers? Vizard says the old rocker tips
at the valve and maybe the shaft is worn to match the current lift. He
says if I change the lift, I need to get new rockers.
So the question is -- do I have a valve guide wear problem at .425 lift
with standard 1.45:1 rockers -- again it's a street engine -- 3000 miles
per year.
Don
"Navarrette, Vance" wrote:
>
> Don:
>
> The smaller lateral valve loadings are only part of the advantage.
> The frictional losses associated with rotating the rocker around
> the rocker shaft also are eliminated, and the frictional losses
> at the rocker tip are eliminated.
> The net result is more power by virtue of the reduced
> losses. Reduced lateral loadings on the valves and extended
> valve guide wear are just gravy. If you are a racer, you also
> appreciate the fact that roller rockers can function with
> reduced or no lubrication, which means a bullet proof top end.
> Roller rockers also tend to be much more accurate, so
> that cylinder to cylinder matching is improved. This allows
> you to push the whole setup to the hairy edge of detonation
> without one cylinder acting up before the others. This is
> improved margin for 'pushing the envelope' for the gear heads
> out there.
> The disadvantage is cost, as always.
>
> Cheers,
>
> Vance
>
> ------------------------------
> 1974 Mimosa Yellow Triumph TR6
> Cogito Ergo Zoom
> (I think, therefore I go fast)
>
>
> -----Original Message-----
> From: Don Malling [mailto:dmallin@attglobal.net]
> Sent: Tuesday, January 07, 2003 6:54 PM
> To: 6-Pack
> Subject: Valve lift and lateral forces on the valve guides
>
> List,
>
> I understand that one of the advantages of roller rockers is that they
> reduce or eliminate lateral forces on the valve guides at higher valve
> lifts.
>
> At what valve lift does this become important? For example, if I have a
> cam with .425 valve lift using stock 1.45:1 rockers, do I have a
> problem? How much valve lift can I have before I start needing roller
> rockers. I understand this is not a binary thing -- If I have a little
> too much lift I will have a little too much wear. Lots of lift, means
> lots of wear. I have no feel for the range -- little problem to big
> problem.
>
> Thanks,
>
> Don Malling
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